The Stevenson Screen is a standard housing for meteorological thermometers.
The screen is naturally ventilated with double-louvred sides which serve to
shield the instruments from direct sunlight and precipitation but allow an airflow
over the sensors. The screen is painted white to reduce the effects of heating
by solar radiation. The screen is located in as open a location as possible
such that the thermometer sensors are 1.25m above the ground. As far as possible
the ground cover beneath the screen should be short grass.

The screen was devised in 1864 by Thomas Stevenson (1818-1887), father
of the writer Robert Louis Stevenson.

Inside the screen are a number of instruments and sensors
Starting top right in the right-hand picture and going clockwise
Temperature sensor (wireless) sending signal to receiver in top room of house
Davis Weather Monitor temperature and humidity sensor(cabled) sending signal
display indoors and then to PC
Kestrel 4000 hand held weather tracker. This measures a range of weather parameters
and is used for checking the accuracy of the other sensors.
Casella thermohygrograph. Something of an old timer this, having been overtaken
by the flood of digital sensors now in use. The thermohygrograph records temperature
and relative humidity. The temperature is measured by means of a bimetallic
strip and humidity is measured by utilising the changes in the length of strands
of human hair as humidity varies. All these changes are transferred by means
of levers and pen arms to two fiber tipped pens on pen-arms which record the
data on a chart wrapped round a rotating drum. The drum is geared to make a
complete rotation in 7 days.